Antifoggant



Patented Sept. 11, 1945' 2,334,593 ANGGANT Frederic B. Bean, Rochester,N. Y5, assignor to Eastman Kodak Company, Rochester, N. E, a corporationof New Jersey No g. Application August 6,1943, Y

. Serial No. 497,637

4 Claims.

This invention relates tophotography and particularly to a photographicfog inhibiting agent. Various compounds have been proposed for use inphotographic emulsions and developers to inhibit the formation of fogupon development of the emulsion. Trivelli and Jensen, in Journal of theFranklin Institute, Vol; 210, 1930, page 287,

proposed the useof I G-nitrobenzimidazole in the developer for thispurpose. Trivelli and Jensen found that fi-nitrobenzimidazole wassuperior to potassium bromide and potassium iodide in hydroquinone,pyrogallol and p-aminophenol developers for inhibiting fog while givingthe least depression of image densities.

The use of G-nitrobenzimidazole nitrate has also been recommendedas ananti-foggant for photographic developers. This compound is a morepowerful anti-foggant than th free base but it has the disadvantagethat, although used in very small proportions in relation to the otheringredients of the developer, it is very sparingly soluble in alkalinesolutions. This gives rise to difllculties, particularly whenincorporated in the dry powder form of phot raphic developers to bedissolved in water for use. Due to the low solubilityof theG-nitrobenzimidazole nitrate and the extremely small amount employed,itis very difflcult to judge when complete solubility has taken place.Because the extremely powerful action 'of this'anti-foggant, thisincomplete solubility frequently leads to erratic behavior andnon-uniform results of the developing solution. If the anti-foggant isnot completely dissolved, the fog inhibiting effect is lower than wouldbe expected, and particles of the compound may eil'ect the emulsionlocally where the come in contact.

agent and. the other containing the-sulfite, carbonate or otheringredients of the developer. If the S-nitrobenzimidazole nitrate isincorporated with the reducing agent, it is unstable and, after 'a shorttime, leads to discoloration and oxidation of the reducing agent. Ifincorporated with the alkali powden'reaction. occurs with the formationof the free base and solubility is greatly lowered.

It is, therefore, an object of the present invention to provide animproved fog inhibiting agent for photographic use. A further object isto provide 'a photographic developing solution which has effective foginhibiting action and greater stability than those heretofore used. Astill further object is to provide a stable dry powder photographicdeveloper having foginhibitor therein. Other objects will appear fromthe following description of ,my invention. 7

These objects are accomplished by employing as the fog inhibiting agentan alkali-metal salt -of fi-nitrobenzimidazole such as the sodium salt.

The alkali-metal salts of G-nitrobenzimidazole such the the sodium orpotassium salts are extremely soluble in water or in alkaline solutionand may, therefore, be rapidly dissolved along with the otheringredients of a photographic developing solution. These salts arebelieved to be formed by substitution of the alkali-metal radical on theNH group of the G-nitrobenzimidazole as-shown in the following formulafor the sodium salt of G-nitrobenzimidazole although I do not wish to berestricted to compounds of this structure if the salt is formed in someother manner:

most advantageously be incorporated with the alkaline powder withoutdeterioration or change occurring during storage. Upon dissolving themixture in water, complete solubility of the sodium salt is obtained anda developer of uniform action is produced.

The following example illustrates a dry powder developer compoundedaccording to my invention:

Grams A. Mononiethyl-p-aminophenol sulfate--- 1 Hydroquinone 8 8. Sodiumsulfite 30 Sodium metaborate 10 Potassium bromide 1 Sodium salt of8-nitrobenzimidasoie.- 0.125

added to about 100 cc. of a solution made up of 32.3 grams ofB-nitrobenzi'midazole and 8 grams of sodium hydroxide. The brilliantlyyellow colored sodium salt precipitated in almost quantitative yield.The salt was filtered off and dried at 50 C.. or above. I

(2) The sodium salt of B-nitrobenzimidazole may also be prepared bydissolving 8 grams of sodium hydroxide in 100 to 150 cc. of water andadding 32.3 grams of B-nitrobenzimidazole to the solution. The solutionis then warmed until the ingredients are completely dissolved and thesolution then evaporated to dryness preferably in vacuum. This gives aquantitative yield of the sodium salt.

For preparation of the potassium salt of 6- nitrobenzimidazole, anequivalent amount of potassium hydroxide is used instead of sodiumhydroxide.

Although I have referred particularly to the incorporation of thealkali-metal salts of G-nltrobenzimidazole in the developing solution,it will be understood that these compounds may also be incorporated inthe silver halide emulsion iuelf.

I claim:

1. A photographic developer containing a silver halide developing agentand a fog inhibiting amount of an alkali-metal salt ofo-nitrobensimidazole.

2. A photographic developer containing a silver halide developing agentand a fog inhibiting amount of the sodium salt of G-nitrobenzimidazole.

3. A dry powder composition for dissolving in water to produce aphotographic developing solution comprising a silver halide developingagent, an alkali and a fog-inhibiting amount of an alkali-metal salt ofB-nitrobenzimidazole.

4. A dry powder composition for dissolving in water to produce aphotographic developing solution comprising a silver halide developingagent,

an alkali and a fog-inhibiting amount of a sodium as salt ofB-nitrobenzimidazole.

mnnnarc a nun.

